It is basically the separation anxiety. The kid does not take the separation from the mother too well. When I joined my new job, my daughter was one and half years old. I took 15 days of joining time and after 15 days when I joined and left my daughter at the preschool, she started crying like crazy. I again had to take 10 days of leave to settle her down. It was a very tough time. at one point I thought I would have to let go of my job, but thankfully, all went fine.
Initially, I thought there might be some problem but when I looked into the matter and found that there was no problem in the school, I realised that it was because of the separation from me that she was behaving that way.
http://www.pbs.org/parents/expert-tips-advice/2015/09/helping-preschoolers-cope-separation-anxiety/
Read more